This is a great question because it has such a powerful answer as we will see. Yes! The gospel was preached in the Old Testament. First let’s examine the word “gospel”. The Greek word “euaggelion” means “a good message”, while the verb form “euaggelizo” means “to announce good news” and is where we get the English word "evangelize". It is referred to in scripture as “the gospel of God”, “the gospel of Christ”, “the gospel of Jesus Christ, the Son of God”, “the gospel of the kingdom”. Sometimes the same Greek word has been translated using other English words. An example is in Luke 2:10.
“And the angel said unto them, Fear not: for, behold, I bring you good tidings of great joy, which shall be to all people.” (KJV) The English words “good tidings” comes from the same Greek word elsewhere translated “gospel.”
This scripture in Luke points out something very important to us, that the “gospel” or “good tidings” is really good news “which shall be to all people”. Now the apostle Paul tells us some important information about this in Galatians 3:8 which says “And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.”(KJV) Paul is saying, this Gospel that we preach, was originally found in the promise God made to Abraham in 2045 BC, about blessing all the families of earth. (Also known as the “Abrahamic Covenant”) You can read about this in Genesis 22. Focusing on Genesis 22:16-18.
“And said, By myself have I sworn, saith the LORD, for because thou hast done this thing, and hast not withheld thy son, thine only son: That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies; And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice.” (KJV)
Because Abraham trusted God so completely God rewarded that trust with the promise that thru his seed or descendant “all the nations of earth” will be blessed. Good News? Oh Yes! Or as Luke put it… “good tidings of great joy, to all people!”
Now, turning back to Galatians 3:29. “And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.” (KJV) This is at the heart of or purpose of the Christian calling. It is a foundation principle of our Christian hopes. That as members of the body of Christ, the Christian church, with Jesus as its head does inherit that promise that God made to Abraham long ago. It is the promise that the seed of Abraham is “the Christ” head and body, Jesus and his Church, who will dispense these blessings upon all resurrected mankind in Christ’s Kingdom. These blessings will come in large measure by teaching the resurrected world about God and how they may return to God as obedient children and gain eternal life. Isaiah 2:2-4.
Yes, the “gospel” was preached in the Old Testament. In fact Acts 3:21 states that the gospel was really contained in the words of all of God’s prophets messages. All spoke of “the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.” (KJV)
It becomes our privilege to search thru these messages and find these expressions of God’s love for his groaning creation. May the Lord bless you in your continued search for more of His glorious truth.